Conventionally there is known a transverse electric field system liquid crystal display device. Examples of the transverse electric field system liquid crystal display device include an in-plane switching (IPS) system and a fringe field switching (FFS) system.
In the IPS system liquid crystal display device, each pixel has a structure in which a comb-shape pixel electrode or a pixel electrode in which a slit is formed and a comb-shape common electrode or a common electrode in which a slit is formed are alternately disposed. On the other hand, in the FFS system liquid crystal display device, each pixel has a structure in which a comb-shape pixel electrode or a pixel electrode in which a slit is formed is disposed on a planar common electrode formed over the pixel.
FIG. 38A is a sectional view illustrating an example of a pixel configuration of a conventional transverse electric field system liquid crystal display device. FIG. 38B is a plan view illustrating the pixel configuration of the conventional transverse electric field system liquid crystal display device in FIG. 38A.
As illustrated in FIG. 38A, the conventional transverse electric field system liquid crystal display device includes a pair of first substrate SUB1 and second substrate SUB2, which are made of a glass substrate, liquid crystal layer LC sealed between first substrate SUB1 and second substrate SUB2, first polarizing plate POL1 disposed outside first substrate SUB1, second polarizing plate POL2 disposed outside second substrate SUB2, and backlight BL. First polarizing plate POL1 and second polarizing plate POL2 are disposed such that a crossed Nicol positional relationship holds. That is, polarization axis POLA1 of first polarizing plate POL1 and polarization axis POLA2 of second polarizing plate POL2 are orthogonal to each other.
Alignment film ORI is formed on an inside surface of first substrate SUB1. Common electrode CT, upper insulator UPAS, pixel electrode PX, and alignment film ORI are formed on an inside surface of second substrate SUB2 in this order. For example, liquid crystal layer LC is formed by positive liquid crystal molecule LCBP.
In the transverse electric field system liquid crystal display device having the above structure, an electric field (transverse electric field EL) substantially parallel to the pair of first substrate SUB1 and second substrate SUB2 is generated between pixel electrode PX and common electrode CT by applying voltage to pixel electrode PX and common electrode CT. Therefore, as illustrated in FIG. 38B, liquid crystal molecule LCBP of liquid crystal layer LC rotates according to initial alignment angle THIN. Specifically, when transverse electric field EL is generated, liquid crystal molecule LCBP rotates from a state of liquid crystal molecule LCBPOFF that is of an initial alignment state to a position of angle THON, and becomes a state of liquid crystal molecule LCBPON. In FIG. 38B, liquid crystal molecule LCBP rotates to right by transverse electric field EL.
Because liquid crystal molecule LCBP is of a positive type, initial alignment angle THIN of liquid crystal molecule LCBPOFF is an angle formed between a 90°-270° line and a long axis direction (initial alignment axis direction) of liquid crystal molecule LCBPOFF existing near a boundary of alignment film ROI. The long axis direction of liquid crystal molecule LCBPOFF is substantially matched with the direction of polarization axis (absorption axis) POLA2 of second polarizing plate POL2. For example, initial alignment angle THIN has a range of 0°<THIN<20°.
Angle THON of liquid crystal molecule LCBPON is an angle formed between the 90°-270° line and the long axis direction of liquid crystal molecule LCBPON during white display when the transverse electric field is provided to liquid crystal molecule LCBP.
Thus, in the transverse electric field system liquid crystal display device, liquid crystal molecule LCBP is rotated in a substrate surface by providing the electric field substantially parallel to first substrate SUB1 and second substrate SUB2 to liquid crystal molecule LCBP. For this reason, in the transverse electric field system, apparent retardation R of liquid crystal layer LC does not change too much even if a visual angle direction changes, but an extremely wide viewing angle is obtained compared with a longitudinal electric field system. Assuming that d is a thickness of liquid crystal layer LC and that Δd is refractive index anisotropy (refractive index difference) of liquid crystal molecule LCBP, retardation R is given by R=Δn·d.